Heretofore, a molded product comprising polyolefin such as polypropylene was often coated on its surface or other resin layer was formed thereon to enhance its additional value. However, generally, since polyolefin does not have a polar group in a molecule, it is poor in adhesion to a paint or other resins. Therefore, heretofore, a polyolefin molded product was previously treated with a primer on its surface to improve adhesiveness and adhesion to a paint, and was coated with a paint. However, most of conventional primers or paints contain an organic solvent or dissolved in an organic solvent, and therefore there were problems that they degraded working environments during production and using.
Under these circumstances, various polyolefinic aqueous dispersions have been recently studied and proposed as a resin for a primer or a paint of a polyolefin molded product.
For example, there are disclosed an aqueous dispersion comprising water, a nonionic surfactant, a thermoplastic resin and a thermoplastic resin containing a carboxylic acid or its salt (JP-B-7-35479), an emulsified material having an adhesive film-formability after coating and drying, which contains an acid-modified amorphous polyolefin and a surfactant as essential components (JP-A-8-176374), an aqueous resin composition containing a modified polyolefin resin, a block isocyanate compound and a surfactant (U.S. Pat. No. 2,622,804), and an aqueous polyolefin resin composition comprising polyolefin and/or modified polyolefin, a surfactant having a polyalkylene oxide structure having a specific solubility parameter, a basic material and water (U.S. Pat. No. 2,769,958), and the like.
However, according to these conventional methods, there were problems that a satisfactory dispersion stability endurable for practical use could not be obtained since a particle size of dispersion particles in an aqueous dispersion was large, and smoothness of its coated film and adhesion to a polyolefin base material were lowered.
An object of the present invention is to provide a polypropylenic aqueous dispersion capable of forming a satisfactory water-resistant coating film having a satisfactory smoothness and a satisfactory adhesion to a polyolefin base material, the dispersion particles of which have a small particle size and a sufficient dispersion stability, and are prepared by using a polymer having appropriate crystallinity and solubility prepared from a starting propylenic polymer and/or a modified polyolefin (hereinafter generally referred to as “propylenic polymer”).